1. Field of the Invention
The present invention relates to a printing apparatus that uses a print head to print an image including characters on a print medium such as printing sheet as it is transported, and more particularly to a printing apparatus in which a drive source for transporting the print medium is also used as a drive source for a print head performance recovery operation for maintaining the function of the print head.
The present invention also relates to a piston pump which drives a piston by a rotary drive force, and more particularly to a piston pump which is suitably applied to a recovery operation for maintaining the function of the print head in the printing apparatus demanded for size reduction and portability.
2. Description of the Related Art
As personal computers, word processors and facsimile machines have come into widespread use in offices in recent years, various kinds of printing apparatus are being offered as information output devices for these equipment. Among these output devices, printing apparatus such as ink jet printers (ink jet printing apparatus) that print images including characters by ejecting ink onto a print medium are well balanced in terms of image quality, print speed, apparatus size and price, and can easily be modified to produce color images. Because of these advantages, ink jet printers are in wide use in a variety of fields.
(Example Construction of Conventional Ink Jet Printer)
FIG. 40 is a perspective view showing a construction of a conventional ink jet printer.
A printing apparatus is generally made up of a combination of different mechanisms. In the ink jet printing apparatus of FIG. 40, a mechanism for feeding and transporting printing media has an automatic paper feed unit 100 for accommodating a plurality of print mediums such as print paper and for separating and feeding one sheet at a time, and a transport unit 200 situated downstream of the automatic paper feed unit 100 in the print medium feeding direction to transport the print medium in synchronism with an image printing. The automatic paper feed unit 100 has a paper feed roller placed in a pressure contact with the top of stacked print mediums and rotated to separate and feed an uppermost sheet. The transport unit 200 has an LF roller 201 driven by a drive source and a pinch roller 202 driven by the LF roller 201, with the print medium held between the pinch roller 202 and the LF roller 201.
A printing unit 400 has a carriage 401 that reciprocally moves along a guide member in a direction perpendicular to the print medium transport direction. The carriage 401 mounts an ink jet print head 500 that faces a print medium without contacting it. The ink jet print head 500 ejects ink from its nozzles according to image data.
A recovery unit 600 maintains a stable ink ejection performance of the ink jet print head 500 by removing viscous ink and dirt adhering to nozzle openings of the ink jet print head 500. The recovery unit 600 has a capping unit 601, a wiping mechanism and a suction mechanism to prevent drying and evaporation of ink from the nozzle openings of the ink jet print head 500. The capping unit 601 has a cap to cap a surface of the ink jet print head 500 formed with nozzle openings (referred to as a “nozzle face”) when it is not printing. The wiping mechanism removes ink adhering to the nozzle face of the ink jet print head 500 as by a blade. The suction mechanism sucks out viscous ink from the nozzles of the ink jet print head 500 and nearby portions through the cap of the capping unit 601. The suction mechanism introduces a negative pressure from a pump into the cap engaging the nozzle face to draw out waste ink not contributing to the printing of images from the nozzles into the cap.
Such a conventional printing apparatus, as described in Patent References 1 and 2(listed below), is known to have a construction in which a plurality of drive mechanisms are driven by a second drive source separate from the drive source for the print head mounting carriage and in which a proper driving force from the second drive source is selected for output according to the position of the moving carriage. For example, in the case where a recovery mechanism and a sheet feeding mechanism are driven by the second drive source, the second drive source is selected for output to these mechanisms according to the position of the moving carriage or a registration operation during sheet feeding is activated or deactivated according to the position of the moving carriage. Patent Reference 3 discloses a construction in which the cap in the recovery unit is slid is to open and close the nozzle face according to the movement of the carriage.
Patent Reference 4 discloses a construction in which a third drive source, separate from the drive sources for the carriage and the print medium transport mechanism, activates the wiping operation, suction operation and paper feeding operation in the recovery unit. It is also described in Patent Reference 4 that the wiping operation and the suction operation in the recovery unit are selectively executed or one of a plurality of paper feeding mechanisms is selectively driven according to the position of the print head mounting carriage and the rotary direction and amount of rotation of the third drive source.
[Patent Reference 1]
Japanese Patent Application Laid-open No. 2001-058731
[Patent Reference 2]
Japanese Patent Application Laid-open No. 2001-058742
[Patent Reference 3]
Japanese Patent Application Laid-open No. 2000-135794
[Patent Reference 4]
Japanese Patent Application Laid-open No. 11-138782(1999)
The constructions disclosed in Patent References 1–4, however, change an output destination of the driving force according to the operation of the carriage and therefore have the following problems.
The constructions disclosed in Patent References 1 and 2 require a relatively complex mechanism to switch the output destination of the driving force and take an additional time to move the carriage to the switching operation position and to execute the switching operation. In addition, the switching operation position needs to be provided outside the normal movement range of the carriage. This raises a problem of an increased apparatus body size in the carriage movement direction. These problems are also found with the construction shown in Patent Reference 3.
Further, the construction of Patent Reference 4 requires a complex mechanism for each of the wiping, suction and paper feeding operations to switch the output destination of the driving force of the third drive source. Furthermore, the problems still remain that the switching operation according to the position of the moving carriage takes an additional time and that the size reduction, simple construction and low cost are compromised.
(Example Construction of Pump in Conventional Printing Apparatus)
Printing apparatus with functions of printers, copying machines and facsimile machines, and printing apparatus used as output devices for composite electronic devices including computers and word processors and for workstations are constructed to form images on print mediums (recording medium) such as paper, thin plastic sheets, etc., according to image information. These printing apparatus may be classified into an ink jet system, a wire dot system, a thermal system and a laser beam system according to the printing method employed.
The printing apparatus may also be grouped into a serial type and a line type in terms of a printing action. In the serial type which employs a so-called serial scan method, a print head (printing means) is scanned in a main scan direction that crosses a sub scan direction in which a print medium is transported. In this type of printing apparatus, a print head is mounted on a carriage that moves along the print medium in the main scan direction, a print medium is set at a predetermined printing position, and then the print head is moved together with the carriage in the main scan direction to print one line of image. After one line of image is printed, the print medium is fed a predetermined distance in the sub scan direction and then the next line of image is printed on the print medium. This printing action and the paper feeding action are alternately repeated to print on an entire print area of the print medium.
In the line type, printing is done without moving the print head in the main scan direction. This type of printing apparatus uses an elongate print head that spans an entire width of the print area of the print medium. After the print medium is set at a predetermined printing position, an image is continuously printed by the print head as the print medium is fed in the sub scan direction.
Of these printing apparatus, an ink jet printing apparatus performs printing by ejecting ink from a printing means (print head) onto a print medium. The ink jet printing apparatus has many advantages, such as an ease with which the printing means can be reduced in size, an ability to print a high resolution image at high speed, an ability to print on plain paper without having to apply a special treatment to it, a low running cost, low noise realized by a non-impact printing, and an ease with which a color image can be printed using multiple color inks. In a line type ink jet printing apparatus which uses a full multi-type printing means (print head) having a large number of nozzles arrayed in a width direction of the print medium, a further increase in the printing speed can be achieved. Particularly, in an ink jet type printing means (print head) that uses thermal energy to elect ink, electrothermal transducers, electrodes, liquid path walls, a top wall, etc. are formed in a substrate through a semiconductor manufacturing process including etching, evaporation and sputtering to arrange ink ejection nozzles and liquid paths in high density. This in turn leads to a further reduction in the overall size of the printing means.
The ink jet printing apparatus generally performs a recovery operation to maintain or recover a stable ink ejection performance. The recovery operation includes a wiping operation for removing viscous ink and paper dust adhering to nozzle openings of the print head and nearby portions, a suction operation for sucking out viscous ink and bubbles from within the print head, and a preliminary ejection operation for ejecting viscous ink from those nozzles that were not activated during the printing operation. During the suction operation a large volume of ink not contributing to the image printing is drawn out by suction and discharged as waste ink. The suction operation uses a negative pressure to forcibly discharge ink from the nozzles. A recovery device for performing this suction operation includes a pump for generating a negative pressure. As the negative pressure generating pump, a so-called tube pump that squeezes a tube with a roller and a piston pump that drives a piston in a cylinder may be used.
FIG. 42 is a partly cutaway perspective view of a conventional tube pump installed in the recovery device of the printing apparatus.
A roller holder 1 rotates to cause rollers 2 rotatably mounted on the roller holder 1 to squeeze a tube 4 installed inside a tube guide 3 to generate a negative pressure in the tube 4. In the tube pump of a type that squeezes the tube 4 with the rollers 2, the tube 4 needs to be put in a cylindrical tube guide 3 about 20 mm in radius to prevent a possible buckling of the tube 4. This type of tube pump therefore is not suited for reducing an overall size of the recovery device. This tube pump, however, has an advantage of being able to easily change a suction volume and a suction speed. A piston pump on the other hand has an advantage that it is suited for a size reduction of the recovery device since the piston pump uses a cylinder only about 10 mm in inner diameter.
The piston pump generates or releases a negative pressure by a reciprocal motion of a piston shaft. Therefore, a drive mechanism for the piston pump conventionally incorporates a variety of conversion mechanisms for transforming a rotary motion of a motor as a drive source into a reciprocal motion.
FIG. 43 and FIG. 44 are perspective views showing different constructions, of a cam mechanism that reciprocally moves a piston 625 in a cylinder 624 of the piston pump.
In a cam mechanism of FIG. 43, a rotating shaft of a cam 5 and a piston shaft 626 cross each other at right angles, while a cam mechanism of FIG. 44 has the rotating shaft of the cam 5 and the piston shaft 626 arranged parallel to each other. The piston shaft 626 is allowed by the cylinder 624 to perform only a reciprocal motion. As the cam 5 continues to rotate in one direction, a driving force is transmitted from the cam 5 through a projection 6 to the piston shaft 626, which repetitively performs a reciprocal motion. The cam mechanisms of FIG. 43 and FIG. 44 both have a simple driving method though the cam portion tends to be larger than the pump portion.
FIG. 45 is a partial cross section showing a construction different from those of FIG. 43 and FIG. 44, as a mechanism for reciprocally driving the piston 625 in the cylinder 624 of the piston pump.
In FIG. 45, the piston shaft 626, which is reciprocally movable in the direction of arrows A1, B1, is made unrotatable about its axis. The piston shaft 626 has a screw groove 7 and a screw cam 8 has protrusions that engage the screw groove 7, so that the piston shaft 626 reciprocates according to the rotating direction of the cam 8. That is, as the cam 8 rotates in one direction, the piston shaft 626 moves in the direction of arrow A1. When the cam 8 rotates in the opposite direction, the piston shaft 626 moves in the direction of arrow B1. The use of such a screw mechanism allows for a size reduction of the cam 8. However, to reciprocate the piston shaft 626 requires repetitive rotation of the cam 8 and It is also necessary to control the amount of rotation, making this driving method complex.
In recent years there are growing demands on the ink jet printing apparatus for a smaller size and an improved portability. To meet these demands, it is necessary keep the height (thickness) of the printing apparatus body low. Therefore, the usefulness of the piston pump that can be reduced in size increases. It is also necessary to simplify the construction of the drive mechanism while realizing a greater size reduction than is possible with the conventional apparatus.